The overall objective is to elucidate the mechanisms which regulate the expression of mitochondrial and nuclear genes during the life cycle of African trypanosomes and explore the mechanisms which coordinate these genetic regulatory processes. The immediate objectives are to characterize the expression of mitochondrial (maxicircle) and nuclear genes at the levels of transcription, transcript processing, and translation. The expression of mitochondrial and nuclear genes will be examined at these levels in different life cycle stages and stocks of Trypanosoma brucei to discern the mechanisms regulating these cell differentiations. Experiments are proposed to: 1. Characterize maxicircle transcripts that are diferentially expressed during the life cycle and those which differ among stocks. These experiments are designed to elucidate the mechanisms that regulate the differential expression of maxicircle genes that was discovered during the previous grant period and the mechanisms of maxicircle transcription and transcript processing. 2. Identify proteins encoded by the maxicircle and characterize their production in different life cycle stages. These experiments are designed to establish the relationship between the presence of specific maxicircle transcripts and mitochondrial proteins and hence mitochondrial function. 3. Identify and characterize nuclear genes that are differentially expressed during the life-cycle. Gene encoding proteins with varying physical and functional associations with proteins encoded by the maxicircle will be studied. 4. Characterize the expression of nuclear genes that are differentially expressed during the life cycle at the genomic level and at the levels of transcription, transcript processing and translation. These studies will be done in parallel with analogous studies of maxicircle genes in order to elucidate the genetic regulatory mechanisms that coordinate the control of these two genetic systems.